1. Field of the Invention
The present invention generally relates to a motor servo system. More specifically, the present invention relates to a motor servo system which can be utilized in a servo system for suppressing irregularity of an FG signal which is generated by a drum motor of a VTR and causes rotation irregularity, or a servo system for controlling a motor such as a capstan motor of a VTR, in which desired responsibility cannot be obtained due to coggings, change of load, and so on.
2. Description of the prior art
As a conventional motor servo system 1 by which the irregularity of an FG signal (hereinafter, simply called as "FG irregularity") can be suppressed, in order to remove a signal component of the FG irregularity from a motor control signal, there was a circuit in which an analog notch filter 2 is inserted as shown in FIG. 7, or a circuit in which a digital notch filter 3 is inserted as shown in FIG. 8. In addition, as the digital notch filter 3 shown in FIG. 8, a circuit as shown in FIG. 9 can be utilized, for example.
In addition, as a conventional motor servo system 1' for controlling a capstan motor 4 of a VTR, there was an circuit as shown in FIG. 10, in which a speed detection and a phase detection are performed on the basis of the FG signal, and these detection signals are synthesized with each other, and thereafter, a motor control signal is applied to the capstan motor 4 through a low-pass filter portion 5, D/A converting portion 6, and etc.
In the analog notch filter 2 utilized in the motor servo system 1 shown in FIG. 7, there is a case where deviation occurs in a center frequency of a notch due to fluctuation of an electronic parts, and therefore, an effect of the notch is decreased.
In addition, in the digital notch filter 3 utilized in the motor servo system i shown in FIG. 8, no deviation occurs in the center frequency, but a RAM time and a CPU time become very long. Especially, in a case where the digital notch filter is utilized for removing the FG irregularity of the drum, the larger sampling times for one rotation, the larger number of delay times, and therefore, the CPU time becomes large. On the other hand, in such a system where a servo control microcomputer and a system control microcomputer are included in the same microcomputer, since the CPU time cannot be dedicated only by the servo control microcomputer, it is impossible to increase enough the sampling frequency by the servo microcomputer, that is, the number of delay times of the notch, and therefore, sufficient security cannot obtained.
Furthermore, in a case where a motor having large coggings or a large change of load is controlled by the motor servo system 1' shown in FIG. 10, although it is necessary to make a servo gain very large, in the past, there was not a way other than a way wherein the servo gain is increased by increasing the sampling frequency. However, when a motor is miniaturized, there was a problem that the coggings or the change of load becomes large, on the other hand, the sampling frequency decreases because the number of magnetization of the motor is decreased, and therefore, it is impossible to suppress enough the irregularity of the rotation of the motor.